1. Technical Field of the Invention
The present invention relates to an optical disc apparatus in which an optical pickup and a main circuit board with a signal-processing circuit are interconnected via a flexible printed-wiring board. The invention relates more particularly to a technique for preventing the optical pickup and the flexible printed-wiring board from sticking to each other.
2. Description of the Related Art
The adoption of thinner optical disc apparatus structures in recent years has shortened the distance between an optical pickup and a flexible printed-wiring board which interconnects the main circuit board and the optical pickup. Accordingly, contact with the planar section of the optical pickup's bottom cover member and the flexible printed-wiring board is becoming prone to occur during movement of the optical pickup. Contact could result in the planar section of the optical pickup's bottom cover member and the flexible printed-wiring board sticking to each other. FIGS. 7A, 7B are explanatory diagrams of mutual sticking between an optical pickup 12′ and a flexible printed-wiring board 17′. For a thin optical disc apparatus, the distance between the surface of the bottom cover member 12c′ of an optical pickup 12′ and the surface of the under cover 18′ of a unit mechanical section is shortened to about 0.7×10−3 m, for example, and the flexible printed-wiring board 17′ with a thickness of about 0.2×10−3 m, for example, is disposed in that space.
Movement of the optical pickup 12′ in approximately the radial direction of an optical disc in that condition also moves the fold-back portion of the flexible printed-wiring board 17′ and the associated portion of the optical pickup 12′. During the movement of the fold-back portion, the portion of the flexible printed-wiring board 17′ that is located on the under cover 18′ will change in position and easily move upward to leave the surface of the under cover 18′. If this actually occurs, the surface of the portion of the flexible printed-wiring board 17′ that is located on the under cover 18′ will come into contact with the surface of the bottom cover member 12c′. For example, if the bottom cover member 12c′ is constructed of, for example, phosphor bronze to obtain the heat radiation property of the optical pickup 12′ and has a smooth surface (with surface roughness less than 0.5×10−6 m, for example), the above contact could result in the flexible printed-wiring board 17′ and the bottom cover member 12c′ sticking to each other, as shown in FIG. 7A. In the event of such sticking, the movement of the optical pickup 12′ pulls and damages the flexible printed-wiring board 17′ and/or increases the load applied to the optical pickup 12′ during the movement. Phosphor bronze and other metallic materials with high heat-transfer characteristics are usually used as structural members in an as-rolled smooth surface condition. As shown in FIG. 7B, the increase in the load of the optical pickup 12′ during the movement is prone to damage the portions 12b1′, 12b2′ of the optical pickup 12′ that engage with a guide member 32′. In FIG. 7B, if the flexible printed-wiring board 17′ and the bottom cover member 12c′ stick to each other, load force F1 or F2 will be exerted on the effective central point P of a sticking region A, depending on the moving direction of the optical pickup 12′, and the load force will work as a moment of arm length R upon the above-mentioned engagement portions 12b1′, 12b2′. This moment of arm length R is expected to damage or unusually wear out the respective bearings 12d′ of the engagement portions 12b1′, 12b2′.
Conventional techniques related to the present invention and described in patent literature include the technique described in, for example, Japanese Patent Laid-Open No. 2005-38534. This Publication describes the technique that allows damage to the flexible circuit board of an optical disc apparatus to be prevented by providing a sliding-contact preventing member on the face of an optical pickup's housing that is directed to the flexible circuit board, and reliably maintaining the interval between the above face and the face of the flexible circuit board that is directed to the housing of the optical pickup. The use of this technique prevents the face of the housing from abrading the face of the flexible circuit board. This conventional technique described in the above Publication, however, is intended only to prevent damage to the flexible circuit board (flexible printed-wiring board) due to abrasion during movement of the optical pickup. Neither a suppression effect against increases in the movement load of the optical pickup due to mutual sticking between the flexible circuit board and the optical pickup, nor a prevention effect against unusual wear on or damage to the portions that engage with a guide member can be obtained using the above conventional technique. In addition, there is a need to install a sliding-contact preventing member on or in the housing of the optical pickup.
The present invention has been made with the above situation of the conventional technique taken into account. An optical pickup in an optical disc apparatus of the invention is constructed such that while maintaining a heat radiation property under a simplified configuration not increasing the number of parts required, the optical pickup prevents mutual sticking between a flexible printed-wiring board and the optical pickup itself, and hence, damage to the flexible printed-wiring board. The optical pickup is also adapted to suppress increases in a movement load of the optical pickup and prevent unusual wear on or damage to the portions that engage with a guide member.
An objective of the present invention is to provide an optical disc apparatus that solves the problem hereinbefore mentioned and improves reliability of the apparatus.